linux-kernel - RE: [PATCH] ipmi: ipmb: don't allocate i2c

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Date:   Wed, 19 Jun 2019 13:39:20 +0000
From:   Asmaa Mnebhi <Asmaa@...lanox.com>
To:     Arnd Bergmann <arnd@...db.de>, Corey Minyard <minyard@....org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     Vadim Pasternak <vadimp@...lanox.com>,
        Corey Minyard <cminyard@...sta.com>,
        "openipmi-developer@...ts.sourceforge.net" 
        <openipmi-developer@...ts.sourceforge.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] ipmi: ipmb: don't allocate i2c_client on stack

Hi Arnd,

LGTM. 

-----Original Message-----
From: Arnd Bergmann <arnd@...db.de> 
Sent: Wednesday, June 19, 2019 8:51 AM
To: Corey Minyard <minyard@....org>; Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Arnd Bergmann <arnd@...db.de>; Asmaa Mnebhi <Asmaa@...lanox.com>; Vadim Pasternak <vadimp@...lanox.com>; Corey Minyard <cminyard@...sta.com>; openipmi-developer@...ts.sourceforge.net; linux-kernel@...r.kernel.org
Subject: [PATCH] ipmi: ipmb: don't allocate i2c_client on stack

The i2c_client structure can be fairly large, which leads to a warning about possible kernel stack overflow in some
configurations:

drivers/char/ipmi/ipmb_dev_int.c:115:16: error: stack frame size of 1032 bytes in function 'ipmb_write' [-Werror,-Wframe-larger-than=]

There is no real reason to even declare an i2c_client, as we can simply call i2c_smbus_xfer() directly instead of the i2c_smbus_write_block_data() wrapper.

Convert the ipmb_write() to use an open-coded i2c_smbus_write_block_data() here, without changing the behavior.

It seems that there is another problem with this implementation; when user space passes a length of more than I2C_SMBUS_BLOCK_MAX bytes, all the rest is silently ignored. This should probably be addressed in a separate patch, but I don't know what the intended behavior is here.

Fixes: 51bd6f291583 ("Add support for IPMB driver")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/char/ipmi/ipmb_dev_int.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/drivers/char/ipmi/ipmb_dev_int.c b/drivers/char/ipmi/ipmb_dev_int.c
index 2895abf72e61..c9724f6cf32d 100644
--- a/drivers/char/ipmi/ipmb_dev_int.c
+++ b/drivers/char/ipmi/ipmb_dev_int.c
@@ -117,7 +117,7 @@ static ssize_t ipmb_write(struct file *file, const char __user *buf,  {
 	struct ipmb_dev *ipmb_dev = to_ipmb_dev(file);
 	u8 rq_sa, netf_rq_lun, msg_len;
-	struct i2c_client rq_client;
+	union i2c_smbus_data data;
 	u8 msg[MAX_MSG_LEN];
 	ssize_t ret;
 
@@ -138,17 +138,17 @@ static ssize_t ipmb_write(struct file *file, const char __user *buf,
 
 	/*
 	 * subtract rq_sa and netf_rq_lun from the length of the msg passed to
-	 * i2c_smbus_write_block_data_local
+	 * i2c_smbus_xfer
 	 */
 	msg_len = msg[IPMB_MSG_LEN_IDX] - SMBUS_MSG_HEADER_LENGTH;
-
-	strcpy(rq_client.name, "ipmb_requester");
-	rq_client.adapter = ipmb_dev->client->adapter;
-	rq_client.flags = ipmb_dev->client->flags;
-	rq_client.addr = rq_sa;
-
-	ret = i2c_smbus_write_block_data(&rq_client, netf_rq_lun, msg_len,
-					msg + SMBUS_MSG_IDX_OFFSET);
+	if (msg_len > I2C_SMBUS_BLOCK_MAX)
+		msg_len = I2C_SMBUS_BLOCK_MAX;
+
+	data.block[0] = msg_len;
+	memcpy(&data.block[1], msg + SMBUS_MSG_IDX_OFFSET, msg_len);
+	ret = i2c_smbus_xfer(ipmb_dev->client->adapter, rq_sa, ipmb_dev->client->flags,
+			     I2C_SMBUS_WRITE, netf_rq_lun,
+			     I2C_SMBUS_BLOCK_DATA, &data);
 
 	return ret ? : count;
 }
--
2.20.0